1. Field of the Invention
The present invention relates to an image storage medium capable of storing image data in the form of an electrostatic latent image, and a method of manufacturing the same.
2. Description of the Related Art
There have been known, in the field of medical X-ray radiology, for example, image recording mediums, on which an electrostatic latent image is recorded by the passing therethrough of X-rays, employing photoconductors sensitive to X-rays (such as selenium, etc.) in order to reduce the quantity of X-ray energy a subject is bombarded with, and to improved diagnostic performance; afterwards, systems for reading out such electrostatic latent images have been disclosed (as in for example: U.S. Pat. Nos. 4,176,275, 5,268,569, 5,354,982, 4,535,468, 4,961,209; xe2x80x9c23027 Method and devise for recording and transducing an electromagnetic energy patternxe2x80x9d, Research Disclosure June 1983; Japanese Unexamined Patent Publication No. 9(1997)-5906; xe2x80x9cX-ray imaging using amorphous seleniumxe2x80x9d, Med Phys. 22(12), etc.) More specifically, in U.S. Pat. No. 4,535,468, for example, an image storage medium comprising a relatively thick 2 mm Al, etc. electrode layer on the recording side, which serves as an electrically conductive substrate transparent to the radiation which is to serve as the electromagnetic energy (hereafter also referred to as recording light) to be recorded thereon, on which are formed a 100-500 xcexcm thick recording photoconductive layer having a-Se (amorphous selenium) as a main component, a 0.1-10.0 xcexcm thick middle storage portion (trap layer) formed of AsS4, As2 S3, As2Se3, etc. for trapping the latent-image charge carriers generated within the recording-use photoconductive layer, a 0.5-100 xcexcm thick readout photoconductive layer having of a-Se as a main component, and a 100 xcexcm thick, readout-side electrode layer, which is transparent to the readout electromagnetic radiation (hereinafter also referred to as readout light) and is formed of Au or ITO (Indium Tin Oxide), superposed one on another in that order, is disclosed. Further, in particular, it is advantageous that the favorable hole mobility of the a-Se can be put to use in employing the readout side photoconductor as the positive electrode, and in order to prevent a deterioration of the S/N ratio upon direct injection of charges from the electrodes, an apparatus wherein a blocking layer formed of an organic material is disposed between the readout-side electrode layer and the readout photoconductive layer has been disclosed. That is, this image storage medium is a multi-layer recording medium, which has great dark resistance and readout responsiveness, and is comprised, overall, of a layer formed mainly of a-Se.
Here, to improve the image S/N ratio, because it has been proposed to shorten the readout time required to perform line readout (primarily in the main scanning direction), in which the electrodes of the readout photoconductive layer comprise many elements (straight line-shaped) aligned with the pixel pitch to form stripe-shaped electrodes (as in for example, Japanese Patent Application No. 10 (1998)-232824, by the same author as that of the current application). However, in the storage portion formation of the image storage medium disclosed in aforementioned U.S. Pat. No. 4,535,468, in the final manufacturing process thereof, the readout-use light side electrode layer must be formed after the readout-use photoconductive layer has been formed, making it difficult to form aforementioned stripe electrodes. To form these stripe electrodes, fine processing of the electrodes must be performed using the photo-etching technique employed in the manufacture of semiconductors. In this process, a high temperature (for example, 200xc2x0 C.) is normally required for the process of baking the photo-resist etc., however, the a-Se of the already formed photoconductive layer is not capable of tolerating such high temperatures, and the characteristics thereof are thereby deteriorated.
In addition, if the alkaline developing agent used in the photo-resist developing processes is brought into contact with the a-Se, a harmful gas is produced, and complicated processes are necessary to circumvent the occurrence thereof, whereby prohibitively high costs are incurred.
On the one hand, the applicant of the current application has proposed, in Japanese Patent Application 10(1998)-232824, an image storage medium (static-electricity recording medium) comprising a recording-light side electrode layer, which is transparent to the radiation that is the recording light, formed of SnO2 (Nesa film), a 50-1000 xcexcm thick recording photoconductive layer formed mainly of a-Se, a charge transport layer formed of a-Se, etc. doped with 10-200 ppm of an organic material or chlorine (Cl), for forming at the interface with aforementioned recording photoconductive layer a storage portion that stores the latent-image charge emitted by the recording photoconductive layer, a readout-use photoconductive layer having a-Se as a main component thereof, and a readout-side electrode layer that is transparent to readout light, disposed in that order.
When manufacturing this image storage medium, no definite order in which the layers should be formed has been explicitly stated, and acceptable results have been obtained by forming the layers in the order starting with the recording-side electrode layer, or in the reverse order thereof. However, as the readout-side electrode layer, a Nesa film or other electrical conductor has been provided on a transparent glass support panel, which is used as the positive electrode and has highly fine xe2x80x9ccomb teeth at a pitch corresponding to the pitch of the pixelsxe2x80x9d and xe2x80x9cformed using semiconductor production technology that forms the comb teeth having a sufficiently narrow interspacexe2x80x9d. That is to say, the electrodes of the readout-light side electrode layer are provided as stripe electrodes arranged at intervals corresponding to the pitch of the pixels. In this case, at first, the stripe electrodes are formed on the transparent glass substrate by a photo-etching process, etc., after which the readout photoconductive layer through the recording-side electrode layer are formed in that order. Note that although a value for the pixel pitch has not been given directly, because in medical-use X-ray radiology a high S/N ratio is possible while maintaining image sharpness, the use of a pixel pitch of 50-200 xcexcm is readily apparent to those skilled in the art.
In addition, in Japanese Patent Application 10 (1998)-232824, in the same way as described in aforementioned U.S. Pat. No. 4,535,468, by providing an approximately 500 A blocking layer formed of an inorganic material such as CeO2 between the readout-light side electrode layer and the readout-use photoconductive layer, deterioration of the S/N ratio by the direct injection of positive charges into the readout-side electrode layer is prevented.
On the other had, afterwards, in further discussions the developers of the invention of the present application found the following points regarding the image storage medium of aforementioned Japanese Patent Application 10(1998)-232824:
1) When carrying out manufacture thereof, after forming a comparatively thin 50-200 nm thick film of ITO on the transparent glass layer, it has been possible to adequately form stable, highly fine stripe electrodes of the readout-side electrode layer.
2) Forming the recording photoconductive layer of a-Se at a thickness of 50-1000 xcexcm provides for excellent dark resistance.
3) As the charge transport layer, a stacked layer type comprising a first hole transport layer composed of a thin layer of organic material 0.1-1.0 xcexcm thick forming the condenser onto which electrons are placed, and a second, high-speed hole transport layer, formed of 5-30 xcexcm thick xe2x80x9ca-Se doped with 10-200 ppm of CLxe2x80x9d, which has few hole traps, superposed one on the other, offers excellent readout responsiveness and after-image formation characteristics.
4) Forming the readout photoconductor of 0.05-0.5 xcexcm a-Se provides for excellent dark resistance.
5) If the charge transport layer is a stacked layer-type hole transport layer comprising a first charge transport layer formed of a 0.1-1 xcexcm layer of PVK or TPD, etc. and a second charge transport layer formed of a 5-30 xcexcm layer of a-Se doped with 10-200 ppm of CL, because the first charge layer attains strong insulation properties with respect to the polarized charge of the latent image, and the second charge transport layer attains high-speed transportability of the polarized transport charges, excellent readout responsiveness and after-image formation characteristics are provided, and although the ideal charge transport layer can be obtained, if a 5-30 xcexcm thick layer of a-Se is used instead in aforementioned second hole transport layer, as a comparatively advantageous result, a structure combining the readout photoconductive layer is obtained, and manufacture thereof is simplified.
From the above, the image storage medium disclosed in Japanese Patent Application No. 10(1998)-232824 is seen to be a multi-layered storage medium offering great dark resistance and high-speed readout responsiveness, and which is preferably formed, overall, of one layer having a-Se as the main component.
Also, in Japanese Unexamined Patent Publication No. 2000-284056, the applicant of the present application has proposed an image storage medium capable of providing a level of improvement in performance over the image storage medium disclosed in Japanese Patent Application 10(1998)-232824. The image storage medium disclosed in Japanese Unexamined Patent Publication 2000-284056 comprises a photoconductive member formed between within the readout-side electrode layer or between the recording-side electrode layer and the readout-side electrode layer, for outputting an electrical signal of a level corresponding to the quantity of the charge of the latent image charge stored in the storage portion formed between the readout photoconductive layer and the recording photoconductive layer.
The conducting member can be of any shape, however, it is desirable that the shape thereof be such that it does not affect the process of forming the latent image (movement of latent image charges, storage) when recording, or the process of recoupling the charges when reading, that is, the latent image charge and the reverse charge thereto, the transport charge. For example, for cases in which the conducting member is formed within the recording photoconductive layer or on the surface of the readout photoconductive layer side of the recording photoconductive layer, it is desirable that the photoconducting member be of a shape that does not interfere with the movement to the condenser of the latent image charge generated within the recording photoconductive layer. Further, for cases in which the photoconducting member is formed within the readout photoconductive layer, the charge transport layer or the trap layer, it is desirable that the conducting member be of a shape that does not interfere with the movement to the condenser of the transport charge generated within the readout photoconductive layer. Therefore, holes of a desired square, round, etc. shape can be provided corresponding to the pixels, or a continuous long hole provided along the direction in which the pixels are lined up can be provided.
In addition, for cases in which aforementioned conducting member is disposed within the readout photoconductive layer, it is desirable that the conducting member be transparent to the recording radiation or the radiation for stimulating the recording radiation, be capable of adequately injecting radiation, etc. into the recording photoconductive layer, and not affect the process whereby charges are generated within the photoconducting layer.
Further, an image storage member has been proposed structured so that the readout electrode layer is a stripe electrode comprising a plurality of line-shaped electrodes, aforementioned conducting member is being formed inside the readout electrode layer and is a sub-stripe electrode comprising a plurality of line-shaped electrodes, and aforementioned stripe and sub-stripe electrodes are disposed alternating and substantially parallel within the readout electrode layer. Further, for cases in which an image storage medium comprises a single electrode formed of a single line of pixels, or a plurality of aforementioned stripe and sub-stripe electrodes, when formed of a plurality of stripe and sub-stripe electrodes, an image storage medium in which the stripe electrodes are of a width more narrow than those of the image storage medium disclosed in aforementioned Japanese Patent Application 10(1998)-232824 has been proposed.
Here, for cases in which the electrodes of the readout electrode layer are stripe electrodes and a blocking layer is provided, normally, after formation of a transparent oxidized film (such as thin film ITO), each element is formed disposed along the pixel pitch by etching, and a blocking layer is superposed thereon by resistance heating vacuum deposition of a film of CeO2.
In this case, because a surface-step is caused between the elements and the transparent glass substrate, the blocking layer is does not cover the side surface of the elements in the lengthwise direction, and the performance of the blocking layer is deteriorated by the injection of a dark current from the side surface of the elements, whereby a problem arises in that the S/N ratio is lowered.
To lower the lengthwise resistance (line resistance) of aforementioned transparent oxidized film of which the elements are formed, there is a method of making it comparatively thick (for example, at a 2000 A thickness), however, as the elements increase in thickness so does aforementioned surface-step, and the deterioration of the performance of the blocking layer becomes conspicuously noticeable.
In addition, for cases in which the readout photoconductive layer comprises aforementioned stripe and sub-stripe electrodes alternating and substantially parallel, a black noise current is produced by the sub-stripe electrodes as well, because this is stored in the condenser as offset noise and becomes a cause of deterioration of the S/N ratio, it is necessary to provide a blocking layer for the sub-stripe electrodes as well. Further, in this case as well, as described above, deterioration in the performance of the blocking layer occurs due to surface-step, and because of the fine pitch owed to the narrowness of the stripe and sub-stripe electrodes, the deterioration is conspicuous. Still further, because it is necessary to provide the sub-stripe electrodes with a cutoff property with respect to the readout light, there are cases in which the electrodes have a greater thickness than that at the time of production thereof, and if the thickness is greater than the thickness of the stripe electrodes (for example, a case in which the stripe electrodes are 0.1 xcexcm thick and the sub-stripe electrodes are 1 xcexcm thick), due to aforementioned surface-step, the deterioration of the performance of the blocking layer becomes even more conspicuous.
The present invention has been developed in light of the circumstances described above, and it is a primary object of the present invention to provide an image storage medium and manufacture method thereof, wherein for cases in which a blocking layer is provided above the stripe electrodes formed on the support body, there is no deterioration in the blocking performance of the blocking layer due to a forementioned surface-step, and further, even for cases in which stripe electrodes and sub-stripe electrodes have been formed alternating and parallel to each other and a blocking layer has been formed thereon, deterioration of the S/N ratio due to dark noise current emitted from the sub-stripe electrodes is prevented, and there is no deterioration in the blocking performance of the blocking layer due to aforementioned surface-step.
In accordance with a first aspect of the present invention, an image recording medium comprising a support body transparent to readout electromagnetic radiation, a first electrode layer (readout-side electrode layer) in which stripe electrodes having a plurality of line-shaped electrodes are disposed in a direction substantially perpendicular to the lengthwise direction of the support body, a readout photoconductive layer that exhibits conductivity upon being irradiated by readout electromagnetic radiation, a storage portion that stores a polarized charge of a latent image, a recording photoconductive layer that emits a polarized charge of a latent image and exhibits conductivity upon being irradiated by recording electromagnetic radiation, and a second electrode layer (recording-side electrode layer) that is transparent to recording electromagnetic radiation, superposed one on the other in that order, wherein between said readout photoconductive layer and said first electrode layer a blocking layer is provided that transmits said readout radiation and blocks injection of charges from each of said line-shaped electrodes, and which is provided so as to cover the top and side surfaces of each of said line-shaped electrodes in a continuous manner.
The expression xe2x80x9cupper surfacexe2x80x9d refers to the surface of the readout photoconductive layer. In addition, the expression xe2x80x9cside surfacexe2x80x9d refers to the two side surfaces of the line-shaped electrodes extending in the lengthwise direction. In this way, all exposed surfaces of each line-shaped electrodes are covered by the blocking layer.
Note that from the standpoint of blocking performance, as described above, it is sufficient if all exposed surfaces of each line-shaped electrode are covered by a blocking layer, however, from the standpoint of the manufacture thereof, it is acceptable if the blocking layer is also formed on the upper surface of the support body between each line-shaped electrode. In this case, the blocking layer is formed as a continuous layer that covers the upper and side of the line-shaped electrodes, and the upper surface of the support body.
Note that in accordance with a first aspect of the image storage medium of the present invention, each of aforementioned layers may be superposed one on the other in the order described above, or as described below, another layer such as a charge transport layer may be formed between aforementioned layers.
In accordance with a second aspect of the present invention, an image recording medium comprising a support body that is transparent to readout electromagnetic radiation, a first electrode layer having a first stripe electrode, formed of a plurality of line-shaped electrodes, that generates photoelectrical charges in the readout photoconductive layer upon irradiation thereof by said readout radiation and a second stripe electrode, that does not generate photoelectrical charges in the readout photoconductive layer upon irradiation thereof by said readout radiation, arranged alternating and substantially parallel, a readout photoconductive layer that exhibits conductivity upon irradiation thereof by said readout radiation, a storage portion that stores a latent-image polarized charge, a recording photoconductive layer that emits said latent-image polarized charge upon irradiation thereof by said recording radiation, and a second electrode layer transparent to said recording radiation, superposed on one another in this order, wherein between said readout photoconductive layer and said first electrode layer a blocking layer is provided that transmits said readout radiation and blocks injection of charges from each of said line-shaped electrodes.
Here, aforementioned xe2x80x9ca first stripe electrode, formed of a plurality of line-shaped electrodes, that generates photoelectrical chargesxe2x80x9d is an electrode that transmits readout electromagnetic radiation and emits charges, and xe2x80x9ca second stripe electrode, that does not generate photoelectrical chargesxe2x80x9d is an electrode that cuts off reading electromagnetic radiation and does not emit charges in the readout photoconductive layer, however it is not limited to being an electrode which perfectly cuts off all readout radiation and emits no charges at all, but can include electrodes that are marginally transparent to readout radiation and emit charges to a degree that causes no substantial problems. Accordingly, all the charges generated in the readout photoconductive layer are not exclusively due to electromagnetic radiation that has passed through the first stripe electrode, but some charges are generated in the readout photoconductive layer due to small amounts of electromagnetic radiation that passes through the second strip electrode as well.
In addition, the xe2x80x9cblocking layerxe2x80x9d of aforementioned image storage medium according to the second aspect of the present invention can be a blocking layer that covers the upper surface of each line-shaped electrode, or as in the image storage medium according to the first aspect of the present invention described above, can cover the entirety of the exposed surfaces (upper and side surfaces) of each line-shaped electrode. Further, the blocking layer can also be formed so as to cover the upper surface of the support body between each electrode. Still further, the material composing the blocking layer covering the upper surface and that covering the side surface do not have to be the same; several materials can be used, as long as they have the blocking property. Therefore, for example, blocking can be performed on the upper surface by a predetermined material, and on the side surface by a different material. Note that for the image storage medium according to the first aspect of the present invention as well, the blocking material of the upper surface and the blocking material of the side surface can be of different materials.
Note that for the image storage medium according to the first aspect of the present invention, each of the layers described above can be superposed one on the other in aforementioned order, or as described below, a charge transport layer or another such layer, etc. may be disposed between any of aforementioned layers.
Also, in addition to having the blocking property, it is preferable that the blocking layer of the image storage mediums according to the first or second aspect of the present invention: have a shock absorbing property enabling it to soften the heat stress due to the difference in heat expansion rates of the first electrode layer and the readout photoconductive layer; be provided so as to function to control crystallization of the interface between the first electrode layer and the readout photoconductive layer, and act as a reinforcing layer adhering between the first electrode layer and the readout photoconductive layer.
In addition, more specifically, it is desirable that the material used to form the blocking layer of the image storage mediums according to the first or second aspect of the present invention be a, polyamide, polyimide, polyester, polyvinyl butyral, polyvinyl pyrrolidone, polyurethane, polymethylmethacrylate, polycarbonate, etc. polymer having insulating properties, or a composite film formed of an organic binder and a lower molecule, etc. thin organic film material having transparency, good blocking properties and resiliency.
Further, the blocking layer can have a thickness of 0.05-5 xcexcm, however, on the one hand, from the standpoint of serving as a buffer to heat stress, the 0.1-5 xcexcm range is preferable, while on the other hand, from the standpoint of leaving no after-image, the range of 0.05-0.5 xcexcm is preferable, and therefore it is desirable to strike a balance between these two factors and employ the range of 0.01-0.5 xcexcm.
Still further, the manufacture method according to the present invention is the manufacture method for the image storage mediums in accordance with the first and second aspects of the present invention, characterized in that the blocking layer is formed by coating the line-shaped electrodes in the lengthwise direction with a blocking layer forming material.
Here, after the stripe electrodes have been formed on the glass or polymer support body, a dip method, a spray method, a bar coating method, or a screen coating method, for example can be employed when coating the line-shaped electrodes along the lengthwise direction thereof with the blocking layer forming material. In particular, through use of the dipping method, by merely dipping the support body having formed thereon the stripe electrodes in a solution and pulling it up and out of the solution repeatedly, even large sizes can be manufactured comparatively simply.
Because the blocking layer of the image storage medium according to the first aspect of the present invention is formed so that it extends continuously over the upper and side surfaces of the line-shaped electrodes, the readout photoconductive layer side of each line-shaped electrode can be completely covered, and injection of the dark current from the first electrode layer of the readout light injection side can be prevented with certainty.
Because a blocking layer is provided between the readout photoconductive layer and the first electrode layer in the image storage medium according to the second aspect of the present invention, not only injection of the dark current from the first stripe electrode, but also injection of the dark current from the second stripe electrode (the sub-stripe electrode) can be prevented.
In addition, if the blocking layer of the image storage mediums according to the first or second aspect of the present invention is formed of an insulating polymer material or a thin film organic material such as a composite film composed of an organic binder and a lower molecule organic material, by use of a simple method of coating the line-shaped electrodes along the lengthwise direction thereof with aforementioned organic polymer material, etc., the thin film can be formed so as to cover with certainty the entire exposed surface of each line-shaped electrode.
Further, according to the manufacture method of the image storage mediums according to the first and second aspects of the present invention, because the blocking layer is formed by coating the line-shaped electrodes along the lengthwise direction thereof with a blocking layer material, inconsistencies in the thickness of the blocking layer occur only in the area at both ends in the lengthwise direction of the line-shaped electrodes. Therefore, because the areas of the ends are normally non-image areas, any negative effect thereof can be avoided. In particular, according to the manufacture method of the image storage medium according to the second aspect of the present invention, even if the line-shaped electrodes are of a narrower width and the difference between the widths of the first stripe electrode and the second stripe electrode is of a large step, the blocking layer can still be easily formed so as to cover the entire exposed surface of each line-shaped electrode.